1. Field of the Invention
This invention relates in general to an aircraft cargo handling system and more particularly to an improved method and device for loading and unloading cargo, both containers and bulk, in an aircraft belly compartment.
2. Background of the Invention
The cargo compartment in the belly of a commercial airliner is typically elongate and semi-circular in cross-section. The curved lower aircraft body structure generally defines both the bottom and side walls of the compartment. A common ceiling height is approximately forty five inches. Because of the low ceiling and curved floor, men cannot easily work in the compartment, and cargo handling is difficult. Manual loading is physically hazardous work. While in a crouched or crawling position, a person must lift and stack forty to fifty pound bags, boxes, and cases. Therefore, other methods have been attempted for belly compartment cargo handling.
One method of belly compartment cargo handling comprises a series of pairs of conveyor belts and rollers mounted on the compartment floor. This method has been used in the Boeing 757. Incoming cargo is placed on a first pair of moving belts which conveys it to a second pair and then to a third pair and so on until the end of the available compartment space is reached. Each pair of belts must have its own motor, gearbox, and clutch, allowing it to be selectively activated so that it does not continue to run after its cargo can no longer move.
This modular belt system has several drawbacks. The system is only practical for standard containers and cannot readily handle bulk cargo. It requires a considerable amount of the usable compartment space. With the many motors and drive components, the system is quite heavy and detracts from the airplane's carrying capacity. It is complex and expensive. Importantly, because the system is modular, if one motor fails, the others must carry the overload. At the least, the cargo remaining on a failed module must be removed by hand.
In another prior art method, referred to here as the telescoping method, a series of successively smaller intersheaved shells lines the compartments. Upon loading, the shells are collapsed to a position adjacent the door opening whereby only the innermost shell is available for loading. After this innermost shell is loaded, it is extended into the compartment which permits the next shell to be loaded, etc. To unload, the cargo in the door area is removed, exposing the largest shell adjacent the door. When the largest shell is unloaded, the remaining shells are telescoped toward the door area and each is unloaded in sequence. The telescoping method is heavy and requires a different shell shape for each aircraft shape. It handles bulk cargo only. The shells take up considerable cargo volume since each shell is approximately one inch thick. The shells are easily damaged and can hang up and otherwise malfunction.
Therefore, it is desirable to have a powered cargo loading system for an aircraft belly compartment which is simple, reliable and can handle both bulk and containerized cargo, singly or intermixed.
It is further desirable that such a system be designed to minimize possible failure modes and that the most failure-prone components can be quickly replaced with minimal cargo removal.
It is further desirable that the system be light weight and require only a small volume. It is further desirable that the system is easily adaptable to the different aircraft shapes using common components.